The known belt tensioners are mostly related to designs that are used in maintaining belt tension in serpentine belt drives for automotive applications. While the majority of the known tensioners pertain to automotive application tensioners, there are other industrial applications where machines have drive systems that have motors driving pulleys with endless belts that need to be tensioned. One example of the prior art is shown in U.S. Pat. No. 4,557,709.
The known belt tensioners are constructed of a base part, a lever arm and a spring. The lever arm has a mounting feature onto which a pulley is attached. The pulley rides against the belt that is to be tensioned. The base is mounted on or in proximity to the device containing the drive belt. The base part contains a feature that houses the spring and also fixes one end of the spring from moving. The base typically has a hole axially through its central area and through the center of the spring that receives a pivot feature on the lever arm.
The lever arm has a pivot feature that usually has a shaft with a hole through it. The arm may also have a feature onto which one end of the spring is affixed. On the lever arm at a distance from and parallel to the pivot axis is a feature where a pulley can be attached. The pulley is forced against the belt and the drive system by the torque from the spring.
The spring in the known art is either a torsion spring or a spiral spring. The spring has one end fixed to the base and the other fixed to the arm. As the arm is moved in a radial manner about the pivot, the base is fixed and does not move, so the end of the spring fixed to the base does not move. The spring is compressed by the radial movement of the lever arm, which stores energy in the spring. The stored energy applies a steady force or torque to the arm and the pulley, pressing the pulley into engagement with the belt. The pulley adds tension in the belt by deflecting the shape of the belt. The added tension maintains the belt in a tight arrangement in the drive system.
A bolt is usually placed through the arm and the hole, through the pivot and base and threaded or fixed to the drive system. The bolt keeps the base from moving relative to the drive system. The pivot feature allows the lever arm to move when the bolt is tightened. The base is mounted so that there is some amount of compression in the spring when the belt is mounted against the pulley. As stated earlier, this compression exerts torque on the lever arm to press the pulley into engagement with the belt. The pulley maintains tension in the belt and compensates for changes in the length of the belt. When slack develops in the belt due to belt expansion or stretching, the spring has sufficient stored energy to exert additional torque on the lever arm and press the pulley further into the belt to remove any slack.